Means for prolonging balloon flight



ma k F Sept. 15, 1959- w. F. HUCH 2,904,285 MEANS FOR PROLONGING BALLOON FLIGHT Filed June 29, 1956 INVENTOR.

WILLIAM F. HUGH ATT'Y United States Patent Ofiice 2,904,285 Patented Sept. 15, 1959 NIEANS FOR PROLONGING BALLOON FLIGHT William F. Huch, St. Paul, Minn., assignor, by mesne assignments, to the United States 'of America as represented by the Secretary of the Navy Application June 29, 1956, Serial No. 595,035

2 Claims. (Cl. 244-31) This invention relates to balloons and is concerned more particularly with the duration of balloon flight.

A constant volume (i.e., inelastic or non-extensible) balloon made of plastic such as a polyester film or other suitable material and containing lift gas will normally lose lift slowly due to the escape of the gas by leakage through the balloon material due to imperfection in the material or the sealing thereof. Further slow loss will occur due to'diffusion of the lift gas through the balloon material.

Accordingly the balloons time aloft in many cases is not as long as desired.

Various relatively expensive and/or complex mechanisms have heretofore been developed for prolonging the flight of balloons. These involve among other things modification of the balloon structure or loading the balloon with ballast and automatic means for paying out the ballast intermittently in response to definite increases in atmospheric pressure and at a rate to compensate intermittently for the steady loss of lift.

An object of the present invention is to inexpensively prolong the flight of balloons.

Another object is to provide for continuous slow reduction in weight of a ballasting system supported by the lift gas, by absorption of thermal energy, contemporaneously with continuous inherent gradual loss of balloon lift.

A more particular object is to prolong a balloon flight by evaporation of an inexpensive substance carried aloft by the balloon.

It is also an object to provide a relatively inexpensive means and method for substantially fully or approximately compensating for normal loss of balloon lift from a balloon to maintain the balloon substantially or approximately at ceiling altitude for a predetermined period of time.

A further object is to provide a simple inexpensive automatic means and method employing the principle of evaporation for slowly decreasing the gross weight of a balloon flight to maintain a constant volume balloon approximately at ceiling altitude for a predetermined period of time in cases where a small loss of lift normally occurs due to leakage and diffusion of the lift gas through the balloon envelope.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings, the single figure of which shows more or less schematically an illustrative embodiment of a balloon assembly in accordance with the invention.

Referring now more particularly to the drawing, disclosing an illustrative embodiment of the invention, there is shown in flight at a balloon from which is suspended as by a line 12 a box 14 which may contain telemetering instrumentation and/or material to be automatically released over a target area. The balloon 10 is of the constant volume type formed of a plastic film such as Mylar or polyethylene or other suitable material, and any suitable lift gas may be used although helium is preferred for safety reasons.

The rate of leakage and diffusion of the helium through the balloon material, for example plastic film, is low and be readily calculated for ideal conditions, and the loss of lift from leakage and diffusion under actual conditions from experience of a number of flights has been determined with fair accuracy. In accordance with the present invention this loss of lift is fairly accurately compensated for by evaporation of a suitable substance 18 suspended from the balloon and held in a suitable container 20 having a vent 22. The container 20 is preferably a good heat conductor and may be colored as de sired for absorption or reflection of heat, and may be rigid or may be made of flexible material such as a plastic bag. The substance 18 may be Water, alcohol, liquid air, or other suitable liquid which is evaporative under the conditions of balloon flight, or it may be an evaporative solid such as one which evaporates by sublimation. An example of such a solid is carbon dioxide, commonly called Dry Ice. The quantity of any selected evaporative substance to be used can be calculated for any flight to be made, taking into consideration, among other things, the net absorption by the container of solar radiation energy, the anticipiated rate of loss of lift, the physical properies of the substance, the area thereof exposed to evaporation, coloration of the container, the terrestrial heating effects after sundown, and the length of time it is desired to prolong the flight of the balloon. The container and contents, and the container-suspending line, together constitute a ballasting system which undergoes loss of weight by evaporation of the substance 18. If the rate of loss of weight by evaporation equals or exceeds the rate of loss of lift, the balloon will remain approximately at a predetermined ceiling altitude substantially as long as any of the substance 18 remains. Generally, when Dry Ice is used, anywhere up to about 10 pounds of such substance is employed, although the quantity may be greater for conditions requiring it. Evaporation is of course accompanied by loss of heat, which is supplied by radiation and conduction.

The invention is of course useful with any balloon which undergoes loss of lift for the reasons mentioned, but it is particularly advantageous where expense is an important item and the greater accuracy of the more expensive compensating devices is not required. In cases Where inexpensive balloon envelopes are used, such for example as the so-called pillow balloon, a common size of which is about square when deflated, and where the degree of accuracy of compensation afforded by evaporation is sufiicient for the use to which the balloons are to be put, the invention due to the cheapness of evaporative substances and containers therefor is particularly useful.

If it is desired to enclose in the box 14 material to be released over a predetermined target area, any suitable inexpensive means could be employed either when or after the evaporative substance is completely evaporated or at a predetermined time before complete evaporation to release the contents of the box. Such means could be of any conventional or other character and forms no part of this invention.

It is apparent from the foregoing that the invention provides a very inexpensive means and method of maintaining a balloon at approximately ceiling altitude and thereby prolonging the flight of the balloon for a predetermined period of time. This time may be up to a few hours or even a day or longer if desired. Where the ceiling altitude of the balloon is in regions of prevailing 3 winds, it is apparent that with the invention prolongation o'f flig'ht results in increase in range from launching site to target area, from a short distance to a matter of hundreds and even thousands of miles, particularly where at the selected ceiling altitude the winds reach velocities of hundreds of miles .per hour. Where the selected ceilpresent invention are possible in the -light of the above teachings. It is therefore to be understoodthat within the scopeof the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. In a'high altitude balloon system having a predetermined ceiling altitude and comprising -a substantially inextensible film enevlope having a slight permeability to liftgas and-inflated with said lift gas, and subject throughout its flight to continuous normal loss of lift at a predetermined rate by reason of said slight permeability, means carried by said envelope for contemporaneously compensating only for said normal loss of lift, saidmeans comprising a container carried by said envelope, said container having a vent therein open to the atmosphere, a quantity of non-gaseous 'highly evaporative substance in said container, the size of said vent being calibrated in conjunction with said substance and the relative permea bility of said envelope, the area of exposure to the atmosphere and vapor 'p'r'essu'r'eof said substance at flight altitudes and temperatures being sufiiciently great to insure loss of weight of said substance by evaporation to the atmosphere through said "vent "simultaneously with and at a rate such as to 'atleast compensate for'said normal loss of lift for'a'predete'r'minedperiod df'ti'rhe after the balloon-system'first reaches ceiling altitude, said time being dependent upon the quantity ofevaporative substance.

2. The structure of claim 1, characterized in that the only heat sources for the substance are solar radiation energy and terrestrial r'adiation energy.

References Cited the file'of this patent UNITED STATES PATENTS 

